1. Field of the Invention
This invention generally relates to data storage in data processing systems and more particularly to a method for copying data from one storage device to another storage device.
2. Description of Related Art
Copying data from one location, commonly a “source location” to a second or “destination location” is well known in the art. In some situations copying provides data redundancy. In other situations providing two or more copies enables a like number of independent applications or procedures to process the copied data independently.
In one conventional approach, as particularly well known in the use of personal computers, copying is performed on a file-by-file basis between different logical volumes or between different directories on the same logical volume. The conventional device utilizes a “copy” command that specifies a path to a source and file to be copied and a path to a destination location. The processor then copies the data from the source to the location. During the copy process no application can access the data at either the source location or the destination location.
In other systems involving larger and more sophisticated data storage facilities, applications may operate on multiple host processors. Such facilities often have the capability of performing copying independently of other host applications. That is, while data is being copied from a source to a destination, other programs or processes can operate on data in locations other than the source or destination file locations. However, in these systems any access to the source file or the destination file is precluded until such time the copy has been completed.
In such systems data can be identified either by physical or logical addresses. Physical addressing includes the identification of device number, a track number and a record number. Logical addressing refers to a logical volume, a file and in some instances a record. Each of these elements has a “granularity”, a term of differing values. For the physical device granularity, from the coarsest to the finest granularity is ranked as a physical disk, a track, a sector and a record; in logical devices, the element ranking is logical volume, file and record.
In the foregoing U.S. patent application Ser. No. 08/842,953 copying is done by logical volume, that is with the coarsest granularity. If it is only desired to transfer a subset of data with a finer granularity, such as a file, such logical volume transfers can produce unnecessary delays. What is therefore needed is a method for copying data from a source to a destination independently of any processor operation with a minimal delay between the processing of a copy command initiating a copy process and the availability of both the source and destination locations for processing by different applications.